用select控件如何触发不了onserverchange事件

用select控件怎么触发不了onserverchange事件？
<select   name= "ss "     id= "ss "   runat= "server "   onserverchange= "ss_change ">
<option   value= "1 "> 1 </option>
<option   value= "2 "> 2 </option>
</select>
这么写对吗？怎么就是触发不了后台代码呢？

------解决方案--------------------------------------------------------
不对.
------解决方案--------------------------------------------------------
还设置postback为true
------解决方案--------------------------------------------------------
<asp:DropDownList ID= "DropDownList1 " OnSelectedIndexChanged= "chg " runat= "server " AutoPostBack= "true ">
<asp:ListItem Value= "1 "> 1 </asp:ListItem>
<asp:ListItem Value= "2 "> 2 </asp:ListItem>
</asp:DropDownList>


------解决方案--------------------------------------------------------
嗯，楼上的都说完了
------解决方案--------------------------------------------------------
要用服务器控制，HTML控件不行的，　用asp:DropDownList　楼上的说的很~~~清楚啦